Pressure fluid operated controlling device



Dec. 31, 1940. H. 2155911 I PRESSURE FLUID OPERATED CONTROLLING DEVICE Filed Sept. 28, 1938 i l nmm Patented Dec. 31, 1940 PATENT OFFICE PRESSURE FLUID OPERATED CONTROLLING DEVICE Herbert Ziebolz, Chicago, Ill., assignor to Askania Regulator Company, Chicago, 11]., a corporation of Illinois Application September '28, 1938, Serial No. 232,243

3 Claims.

This invention relates to improvements in or relating to pressure fluid operated" controlling devices of the type, comprising a servo-motor, a relay controlling a pressure fluid flow to the servo-motor and a so-called isodromic member to exert a restoring effect on the relay.

As is well known, such a restoring effect results in an advantage, to avoid a hunting or over-shooting of the controlling operation.

In such controlling devices it has proved to be advantageous to arrange the isodromic member in the pressure fluid circulation, i. e., in one of the pressure fluid conduits leading from the relay to the servo-motor. Such an arrangement is described in detail for instance in the Patent 1,959,889.

This arrangement, however, necessitates a predetermined dependence of the volume of the isodromic member with regard to the volume of the servo-motor. The isodromic member should have a volume twice as large-as the volume of the servo-motor, as the movement of the isodromic piston out of its middle position into an end position should correspond as much as possible with the entire stroke of the servo-motor piston.

- The invention is based on the idea that this disadvantage may be removed without having to forego the advantages resulting from the arrangement of the isodromic member in the pressure fluid circulation and without having to resort to any artificial means, having defects in any other respect.

Further aims, objects and advantages of this invention will appear from a consideration of the specification which follows 'with the accompanying drawing, showing for purely illustrative purposes two embodiments of this invention:

Referring to the drawing:

Fig. 1 is a diagrammatic illustration of a first embodiment, showing a pressure fluid operated controlling device, comprising a main servo-motor, an auxiliary servo-motor, an isodromic cylinder, and a primary, aswell as a secondary relay.

Fig. 2 shows a second embodiment, according to which the main servo-motor has a modified construction.

Referring now to Fig. l, l are pressure fluid 4 is the isodromic merit-- Germany September 30, 1937 pass I with one another, this by-pass having in a well known manner an adjustable throttle 8. The isodromic piston 5 acts upon a lever Ill, rockably mounted as at 9 to exert a restoring action, on the relay member l2, which is shown in the embodiment according to Fig. l as the Askania jet pipe. Between the jet pipe l2 and the lever ID a spring II is arranged. The jet pipe [2 will be controlled by any convenient controlling impulse produced, for instance by means of a diaphragm capsule schematically shown as at I3. A pressure fluid conduit l4 coming from any suitable pressure source leads to the jet pipe l2 so that the pressure fluid leaving the mouth of the jet pipe enters the receiving nozzles l5 communicating with the conduits I. Therefore, the jet pipe playing in front of the receiving nozzles l5 produces a pressure difference between the two conduits I in accordance with the reflection of the jet pipe from its middle position resulting from the impulse.

If, for instance the diaphragm capsule l3 deflects the jet pipe l2 towards the right, the pressure fluid flow enters the right end of the cylinder 2 and, therefore, displaces the piston 3 towards the left, whilst the pressure fluid passing out of the left end of the cylinder 2 returns through the isodromic cylinder 4 back to the other receiving nozzle IS, the isodromic piston 5 being moved towards the right, resulting in the well known yielding restoring effect with regard to the jet pipe.

The controlling device as described up to now is well known in the art. In such arrangements the piston 3 of the cylinder 2 directly actsupon the member to be adjusted (not shown), for instance a butterfly valve mounted in a gas or liquid conduit to keep constant the flow in this conduit.

Contrary to this well known arrangement, ac,- cording to the invention, the servo-motor 2 acts only as an auxiliary servo-motor by means of which a second relay IE will be controlled, whilst a second servo-motor, i. e., the actual working motor I! is connected to the relay 16 by means of conduits 20, corresponding to the conduits I between the primary relay I2 and the auxiliary cylinder 2. In the illustrated embodiment the. second relay I6 is constructed as a slide valve, whose controlling rod I8 is hinged to a lever l9. This lever is likewise acted upon by the auxiliary piston 3.

In the previously suggested case, in which the piston 3 will be displaced towards the left (due to the deflection of the jet pipe l2 towards the right) the slide valve 5 is also moved towards the left so that the pressure fluid flow coming from the conduit enters the lower conduit 20 leading to the left end of the main motor IT. The piston 2| of this motor is adapted to actuate this member to be adjusted, i. e., in this instance the valve l6, so that the movement of the piston 2| to the right correspondingly displaces the valve l6. For this purpose, the piston 2| is provided with a connecting rod 2 la connected thereto, this rod 2|a being pivotally connected to an arm or link 2|b which, in turn, is rigidly secured to the pivotal axis 220. of a restoring cam 22. This pivotal axis extends through the casing of the servo-motor so that if the piston 2| moves to the left from the position illustrated in Fig. l, the arm 2 lb is moved to produce a movement of the cam 22 in a clockwise direction and vice versa. The upper end of the above mentioned lever I9 is held in engaging relation with the cam 22 by means of a spring 23 and roller [9a. Now if the cam 22 is turned around its axis 220. so as to follow up the movement of the main piston 2| when the latter moves to the right, the lever I9 is rocked in a clockwise manner under the influence of the compression spring 23, thereby restoring the said valve 6. I

In other words, if the piston 3 moves to the left, pilot valve l8 will also move to the left, and thereby uncover line 20, which means that the piston 2| will move to the right. In order to reestablish equilibrium, this movement of piston 2| will operate the cam 22 in a counterclockwise direction, and the spring 23 which keeps contact with the cam surface and the lever I! will move the pilot valve to the right until it is returned to its median position. Thus, a definite relation between "the position of cylinder 3 and piston 2| is established.

From the foregoing it follows that the main piston 2| continuously follows the movements of the auxiliary piston 3. As this piston operates in response to the yieldingly controlled relay ii, the main piston 2| likewise operates in such a manner as if its relay I6 is combined with an isodromic restoring member. On the other hand it is obvious from this arrangement that the dimensions of the isodromic cylinder I and the main or working cylinder I! are in no way re which the piston of the working servo-motor I1 is connected to the cam 22. In this embodiment the restoring cam 22 for exerting a positive restoring action on the secondary relay I6 is pivotally mounted at the cylinder l1 and rigidly connected with the rocking arm 26. The upper end of this arm is pivoted to a controlling rod 25 as at 25b, this rod being likewise. linked to the piston rod 24 of the cylinder H as at 25a.

Otherwise the fundamental structure and the manner of operation is the same as described with reference to Fig. 1.

It is to be noted that the invention maybe used for any isodromic controlling device. However, the inventive idea is especially valuable in from that according to Fig. 1 in the manner in such cases, in which the controlling process op-v erates with great delay, because in these cases (for instance the regulation of the water level in boilers or the like) any temporary inoperativeness of the restoring member is very undesirable due to hunting or over-shooting of the controlling process resulting from such an inoperativeness, which is unavoidable in the well known devices in which theisodromic member is so constructed that in its end position the pressure fluid can freely flow through the isodromic mem her. As soon as this is the case, the restoring operation will be interrupted. The object of this special construction of the isodromic member is to reduce the volume of the isodromic member as far as possible.

In other respects the present invention is also not restricted to the particular embodiments herein shown and described. Moreover, the arrangement and the construction of the individual parts may be modifiedwithout departing from the spirit of the invention as defined in the appended claims.

What is claimed:

1. In a pressure fluid operated controlling device, in combination, a main servo-motor for actuating a member to be controlled, an auxiliary servo-motor having a small pressure fluid volume relative to thatof said main motor, a primary relay connected to control the pressure fluid flow to said auxiliary motor in response to a controlling impulse acting on said relay, a pressure fluid operated restoring motor arranged in the pressure fluid circulation between said relay and said auxiliary motor and connected to exert a yielding restoring action on said relay, a secondary relay mounted to be controlled by said auxiliary motor and to control the pressure fluid flow to said main motor in response to the movement of said auxiliary motor, and restoring means. between said main motor and said sec ondary relay to exert a rigid restoring operation on said secondary relay.

2. In a pressure fluid operated controlling device, in combination, a main servo-motor for actuating a member to be controlled, an auxiliary servo-motor having a small pressure fluid volume relative to that of said main motor, a primary relay connected to control the pressure fluid flow to said auxiliary motor in response to a. controlling impulse acting on said relay, a pressure fluid operated restoring motor arranged in the pressure fluid circulation between said relay and said auxiliary motor and connected to exert a yielding restoring action on said relay, a secondary relay mounted to be controlled by said auxiliary motor and to control the pressure fluid flow to said main motor in response to the movement of said auxiliary motor, a restoring cam connected to be rotated by said main motor for exerting a rigid restoring operation on'said second relay, a restoring lever connected to said auxiliary motor and to said secondary relay and means to hold said .lever in engaging relation with said curve.

3. In a pressure fluid operated controlling device, in combination, a main servo-motor for actuating a member to be controlled, an auxiliary servo-motor having a small pressure fluid volume relative to that of said main motor, a primary relay connected to control the pressure fluid flow to said auxiliary motorin response to a controlling impulse acting on said relay, a pressure fluid operated restoring motor arranged in' the pressure fluid circulation between said relay and said aux a rocking arm, a transmitting rod hinged to said rocking arm and to the piston rod of said main servo-motor for rotating said cam upon a controlling movement of said main motor, a restoring lever connected to said auxiliary motor and to said secondary relay and means to hold said lever in engaging relation with said cam.

HERBERT ZIEBOLZ. 

